The Laṅkāvatāra Sūtra
The Lankavatara Sutra is one of the most important sacred texts of Mahayana Buddhism and has been translated into English by Daisetz Teitaro Suzuki. At the time of this writing, there is no ebook version available, but thanks to the work of Do One there is a HTML version. Thankfully Do One allows free redistribution of his work, so I took the liberty of converting it to the Mobi format which can be read by Kindle. Mobi is an open format, so you should be able to convert it to most other ebook reader formats, for example using a tool like Calibre. Please consider that the original digitizer of this work only allows free redistribution.
Abstract, taken from Wikipedia:
The Laṅkāvatāra Sūtra (Sanskrit: लंकावतारसूत्र Laṅkāvatāra Sūtra; traditional Chinese: 楞伽經; pinyin: léngqié jīng) is a sutra of Mahāyāna Buddhism. The sūtra recounts a teaching primarily between the Buddha and a bodhisattva named Mahāmati ("Great Wisdom"). The sūtra is set in Laṅkā, the island fortress capital of Rāvaṇa, the king of rākṣasas. The title of this text roughly translates as, "Scripture of the Descent into Laṅkā."
The Laṅkāvatāra Sūtra figured prominently in the development of Chinese, Tibetan and Japanese Buddhism. It is notably an important sūtra in Chinese Chán and its Japanese version, Zen.